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From: Shark8 <onewingedshark@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: S-expression I/O in Ada
Date: Thu, 12 Aug 2010 19:31:29 -0700 (PDT)
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Date: 2010-08-12T19:31:29-07:00
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Reading about the Cons-es I figure I should show how the constructs I
made can be made exactly equivalent to a series of Cons-pairs.
Unless I'm completely misunderstanding/misinterpreting the Lisp idea
of a list being an item or an item followed by a list.

     Function Construct_Cons_Pair( Head, Tail : in Node_Type )
                                  Return SExpression_Type is
   begin
      Return Result: SExpression_Type (List_Size => 2) do
         Result.List(1):= New SExpression_Type'( Create(Head) );
         Result.List(2):= New SExpression_Type'( Create(Tail) );
      end return;
   end Construct_Cons_Pair;

     Function Construct_Cons_Pair( Head : in Node_Type;
				   Tail : in SExpression_Type)
                                  Return SExpression_Type is
   begin
      Case Tail.List_Size is
         When 0 => Return Construct_Cons_Pair( Head,
Tail.Data.All    );
         When 1 => Return Construct_Cons_Pair( Head,
Tail.List(1).All );
         When Others =>
            Return Result: SExpression_Type (List_Size => 2) do
               Result.List(1):= New SExpression_Type'( Create(Head) );
               Result.List(2):= New SExpression_Type'( Tail );
            end return;
      end case;
   end Construct_Cons_Pair;


   Function Is_Cons_Pair_Construct( S: in SExpression_Type ) Return
Boolean is
    -- Perhaps this would be better named Is_Lisp_Construct....
   begin
      Return ((S.List_Size = 2) And Then
		((Not Is_List(S.List(1).All)) And
		  Is_Cons_Pair_Construct( S.List(2).All )))
              OR  S.List_Size = 0;
   end Is_Cons_Pair_Construct;

Maybe I should make a Construct_Cons_Pair( Head : in SExpression_Type;
Tail : in Node_Type) for orthogonality's sake... but that would go
against the Lisp-way.